Abstract In this research, we introduce a design of broadband zero-index metamaterials (ZIM). The proposed broadband ZIM comprises two identical layers of octagonal gold exhibiting four-fold rotational symmetry, with a dielectric layer situated in between. Through judicious structural design, we have achieved an equivalent refractive index with the absolute value of its real part less than that of air across a broad bandwidth from 300.6 GHz to 500.4 GHz. By overlaying a 6 × 6 broadband ZIM array atop a terahertz MIMO antenna, we achieved gain enhancements varying from a minimum of 2.6 dB to a maximum of 7.7 dB across four specific frequencies of the terahertz MIMO antenna ( f 1 = 354.2 GHz, f 2 = 394.3 GHz, f 3 = 434.5 GHz, f 4 = 474.8 GHz). In contrast to previous studies that utilized ZIM for antenna gain enhancement, the broadband ZIM developed in this research not only covers a broader operational frequency range but also provides a marked improvement in antenna gain.
Lai et al. (Wed,) studied this question.